The present invention relates to a scanning electron microscope capable of acquiring electron beam image having high resolution in respect of various defect portions present on an object substrate (sample) such as various semiconductor substrates or the like and analyzing characteristic amounts or properties of defect portions based on the acquired electron beam image having high resolution, and a method of analyzing defect portions using the same as well as an automatic image sampling apparatus having a scanning electron microscope preferable for efficiently carrying out review of defects particularly in semiconductor fabrication process.
In recent years, progress of miniaturization of a circuit pattern formed on an object substrate (sample) such as various semiconductor substrates or the like has been remarkable and there is a case in which a defect size of an object to be observed is smaller than the wavelength of light. Hence, in place of optical observation, there has been carried out defect observation using image by a scanning electron microscope. However, when a defect image is taken by a scanning electron microscope, there poses a problem in which even when an object substrate is moved to a position of a defect detected by an appearance inspecting apparatus, the defect which is an object to be observed in the field of view is not present.
The reason is that in addition to a difference in coordinate control between the appearance inspecting apparatus and the scanning electron microscope, an error in accuracy of a sample stage for each of the appearance inspecting apparatus and the scanning electron microscope and so on, the magnification of image taking is much higher than optical magnification in the appearance inspecting apparatus and the field of view is narrow.
Hence, when a foreign particles is observed by a scanning electron microscope, the foreign particle can be discovered most efficiently when low magnification so that a search area is brought into the field of view in one operation, is selected. However, when a size of the foreign particle is small, there is a case that presence of the foreign particle is not noticed with low magnification. Hence, according to Japanese Patent Laid-open No. 5-223747 (prior art 1), in a foreign particle observing apparatus having an optical inspecting device of a foreign particle on a wafer surface and its similar device and an electron microscope for carrying out shape observation or analysis of foreign particle, defects or the like by using wafer coordinates and foreign particle information provided by the devices, there are provided means for determining a level of a size of a foreign particle provided by the optical inspecting device and its similar device and means for dividing an observation area of the wafer into Nxc3x97M of divided areas when the foreign particle level is equal to or smaller than a constant value and dividedly observing the respective divided areas by the electron microscope.
In the meantime, a microscope starting from a scanning electron microscope has various objects of image taking and magnification for taking image thereof has various values. It is very important to take image without causing pseudo noise even under the various conditions. When image is taken manually, an operating person always monitors whether or not pseudo noise is caused in taken image and when pseudo noise is caused, image can be taken again after erasing the noise. However, when observation by the microscope is not carried out manually, for example, when information on positions of a plurality of portions on a sample to be observed is previously inputted to a microscope and the plurality of portions are observed automatically to thereby acquire data of taken image, a control for preventing the above-described noise from being produced is required to be carried out automatically.
However, according to the prior art 1, sufficient consideration is not given to that image is taken without causing pseudo noise in respect of such various object substrates (image taken objects).
Further, according to the prior art 1, it is necessary to enlarge observation magnification to be able to observe fine defects and to search the fine defects over an observation area having Mxc3x97N of the divided areas and wasteful search is obliged to be carried out. In particular, when a number of fine defects are present in an object substrate, an amount of wasteful search is significantly increased.
In order to solve the above-described problem, it is an object of the present invention to provide a scanning electron microscope capable of analyzing characteristic amounts or properties of a defect portion in respect of the defect portion by automatically specifying a position of the defect portion to accurately take an image thereof without generating pseudo noise on a provided digital image even when an image of any object substrate is taken by any magnification and a defect portion analyzing method using the same.
Further, it is other object of the present invention to provide an apparatus and a method of automatically sampling an image by a scanning electron microscope capable of analyzing characteristic amounts and properties (categories) thereof and so on by positioning the fine defect in an image taking field of view of a high magnification in a short period of time to acquire a digital image signal having a high resolution and to take an image of a fine defect with a high magnification.
In order to achieve the above-described object, the present invention is featured in a scanning electron microscope which provides an image taking magnification setting means for setting a magnification of image taking, and takes the image by controlling a spot diameter of irradiating beam on a sample by using information concerning image taking magnification set to the image taking magnification setting unit and background information at an image taking portion.
Further, the present invention is featured in a scanning electron microscope which provides an image taking magnification setting unit for setting magnification of image taking, and carries out a signal processing of a filtering processing or the like to an analog electric signal converted from an intensity of an electron beam signal of secondary electron, reflected electron or absorbed electron from an object substrate (sample) or a digital signal provided from the analog electric signal by using information concerning image taking magnification set to the image taking magnification setting unit and background information at an image taking portion.
Further, the present invention is featured in a scanning electron microscope which includes a switching control unit for controlling to switch at least scanning means so as to be obtained a digital image signal of a low magnification based on a wide image taking field of view and a digital image signal of a high magnification based a narrow image taking field of view being switched from an A/D conversion unit, and a beam spot diameter control unit for controlling to switch a spot diameter of an electron beam at a surface of an object substrate in controlling to switch the signals by the switching control unit or a beam spot diameter control unit for controlling the beam spot of the electron beam based on information concerning a surface texture on an image taking portion of the object substrate in taking an image thereof in a wide image taking field of view by controlling to switch the signals by the switching control unit.
Further, the present invention is featured in a scanning electron microscope which includes a switching control unit for controlling to switch at least scanning means so as to be obtained a digital image signal of a low magnification based on a wide image taking field of view and a digital image signal of a high magnification based on a narrow image taking field of view being switched from an A/D conversion unit, and a control unit for controlling so as to restrain pseudo noise components generated from an image taking portion of an object substrate in taking an image with a wide image taking field of view by controlling to switch the signals by the switching control unit, or a signal processing unit for reducing the pseudo noise components at high frequencies by carrying out a signal processing in accordance with a surface texture of the image taking portion of the object substrate to an analog image signal outputted from a detector or a digital image signal provided by the A/D conversion unit.
Further, the present invention is featured in a scanning electron microscope which includes position specifying means for positioning the defect portion in a wide image taking field of view based on the position coordinate of the defect portion present on an object substrate mounted on a stage, irradiating with the electron beam to scan the positioned defect portion in a defocused state or under a state in which pseudo noise components are restrained from being generated from a background such that a wide image taking field of view is provided, detecting an analog image signal from a detector, converting the detected analog image signal into a digital image signal of low magnification at the A/D conversion unit and specifying the position of the defect portion based on the converted digital image signal indicating the defect portion of the low magnification or the digital image signal indicating the defect portion of the low magnification so that the pseudo noise components at high frequencies are reduced, and analyzing means for positioning the defect portion in a narrow image taking field of view based on the position of the defect portion specified by the specifying means, irradiating with the electron beam to scan the positioned defect portion to provide the narrow taking image field in a focused state, detecting an analog image signal by the detector, converting the detected analog image signal into a digital image signal of the high magnification by the A/D conversion unit and analyzing characteristic amounts or properties of the defect portion based on the converted digital image signal indicating the defect portion of the high magnification.
Further, the present invention is an automatic image sampling apparatus which is a scanning electron microscope including a storing unit for storing a dimension of a defect present on an object substrate provided from an appearance inspecting apparatus and information on a first position coordinate thereof; and a means for positioning a large defect in a field of view of an image taking magnification of a low magnification provided by controlling scanning means based on the information concerning the first position coordinate with respect to the defect having a large dimension present on the object substrate provided from the storing unit, storing a digital signal of the large defect into the image storing unit by taking an image of the positioned large defect by the image taking magnification of the low magnification, calculating a second position coordinate of the defect based on the stored digital image signal of the large defect and calculating a deviation correction coefficient (a coordinate correction coefficient) from a relationship between the calculated second position coordinate and the first position coordinate, and its method.
Further, according to the present invention, there is provided the automatic image sampling apparatus and its method further including image sampling controlling means for calculating a second position coordinate by correcting a first position coordinate of a small defect provided from the storing unit by the deviation correction coefficient calculated by the deviation correcting coefficient calculating means with respect to the defect having a small dimension present on the object substrate provided from the storing unit, positioning the small defect in a field of view of an image taking magnification of a high magnification provided by controlling the scanning means based on information concerning the calculated second position coordinate and storing a digital image signal of the small defect into the image storing unit for sampling by taking an image of the positioned small defect by the image taking magnification of the high magnification.
Further, the present invention is an automatic image sampling apparatus which is a scanning electron microscope including a storing unit for storing a dimension of a defect present on an object substrate provided from an appearance inspecting apparatus and information on a first position coordinate thereof, first image sampling controlling means for positioning a large defect in a field of view of an image taking magnification of a low magnification provided by controlling scanning means based on the information concerning the first position coordinate of the defect having a large dimension present on the object substrate provided from the storing unit, storing a digital image signal of the large defect into the image storing unit by taking an image of the positioned large defect by the image taking magnification of the low magnification, calculating a second position coordinate of the defect and a size of the defect based on the digital image signal of the stored large defect, calculating a deviation correction coefficient from a relationship between the calculated second position coordinate and the first position coordinate, positioning the large defect in a field of view of an image taking magnification adapted to the calculated size of the defect, taking an image of the positioned large defect by the adapted image taking magnification and storing the digital image signal of the large defect into the image storing unit for sampling; and second image sampling controlling means for calculating a second position coordinate by correcting a first position coordinate of a small defect provided from the storing unit by the deviation correcting coefficient calculated by the first image sampling controlling means with respect to the defect having a small dimension present on the object substrate provided from the storing unit, positioning the small defect in a field of view of an image taking magnification of a high magnification provided by controlling the scanning means based on information concerning the calculated second position coordinate, taking an image of the positioned small defect by the image taking magnification of the high magnification and storing a digital image signal of the small defect into the image storing unit for sampling and its method.
Further, the present invention is an automatic image sampling apparatus which is a scanning electron microscope further including a storing unit for storing information concerning a dimension of a defect present on an object substrate and a position coordinate thereof and information concerning a circuit pattern at an area on the object substrate; and a control unit for acquiring information concerning the circuit pattern in an area where the defect is present based on the information concerning the position coordinate of the defect provided from the storing unit and intended to take an image thereof, calculating a restricted image taking magnification restricted based on the acquired information on the circuit pattern, determining an image taking magnification of the defect intended to take the image based on the information concerning the dimension of the defect provided from the storing unit and intended to take the image and controlling scanning means to take the defect of the image intended to take the image by the determined image taking magnification when the determined image taking magnification satisfies the calculated restricted image taking magnification; wherein the image storing unit is constituted to sample and store the digital image signal the image of which has been taken by the image taking magnification adapted to the dimension of the defect.
Further, the present invention is an automatic image sampling apparatus which is a scanning electron microscope including a storing unit for storing information concerning a kind or a classification of an appearance inspecting apparatus and a correlation with an image taking magnification; inputting means for inputting the information concerning the kind or the classification of the appearance inspecting apparatus so that a defect present on an object substrate charged into the scanning electron microscope is inspected; and a control unit for determining an image taking magnification based on the information concerning the correlation stored to the storing unit based on the information concerning the kind or the classification of the appearance inspecting apparatus inputted by the inputting means and controlling scanning means to take an image of the defect present on the object substrate by the determined image taking magnification.
Further, according to the present invention, the automatic image sampling apparatus and its method include analyzing means for calculating characteristic amounts of the defect from the digital image signal of the defect sampled and stored into the image storing unit and classifying properties of the defect by analyzing the calculated characteristic amounts.
Further, according to the present invention, information concerning a dimension of each defect is inputted from an appearance inspecting apparatus to a scanning electron microscope along with information on the position coordinate of defect and since whether position of defect can be recognized in the image of the scanning electron microscope is dependent on a relative dimension in the image of defect, the observing image magnification which is inversely proportional to the dimension of defect continuously or step by step is set and the image of the defect is taken by changing the observation magnification in accordance with the defect dimension. In inputting the image of the deject, by using defects of at least two initial points or more having large defect dimension, deviation of coordinate systems between the appearance inspecting apparatus and the scanning electron microscope is extracted and defect position information thereafter is modified. Thereby, by inputting image with an optimum magnification in accordance with the dimension of the defect, the position of the defect in the image can stably be detected and there can be realized the automatic image sampling apparatus capable of firmly inputting the image for observing the defect.